Stable solutions of compounds of tannins with boric acid



STABLE SOLUTIONS OF COMPOUNDS OF TANNINS WITH BORIC ACID Otto C. Jekel, 1 Freihammerstrasse, Salzburg-Obergnigl, Austria =No Drawing. Filed May 27, 1957, $61. No. 661,593 2 Claims (c1. s 94.33

The present invention relates to new and improved tanning agent solutions and more particularly to stable solutions of boric acid compounds of tannins which are not only suited for tanning animal skins but also and more particularly for topical application to humans and animals in the treatment of disease symptoms caused by fungi and bacteria and known as mycoses.

Solutions of tannins have in the past had the disadvantage of decomposition, changing color and forming solid precipitates after standing a shorter or longer period of time. These phenomena occurred even in the absence of air and light and consequently are independent of the access of air or light. For example, an acetic acid solu tion of tannic acid in n-propanol already becomes cloudy after standing only a few days and assumes a dark color after standing a longer time. The decomposition of such tannin solutions is not readily prevented by chemical means.

According to the invention it was unexpectedly found that solutions of compounds of tannins with boric acid in a solvent mixture of ethyl acetate, ethyl alcohol, acetic acid and water in proportions corresponding to the equilibrium mixture fulfilling the requirements of the law of mass action (Guldberg and Waage, 1879) and containing a maximum of 4% of acetic acid are extraordinarily stable and undergo no or substantially no change even after long periods of standing. Such solutions are not only well suited for tanning of animal skins to produce light leathers, but also for topical application in the treatment of mycoses. It was found that in treatment of mycoses in many instances not only leads to rapid healing but also the treated skin areas become resistant to reinfection.

The equilibrium solvent mixture of ethyl alcohol, acetic acid, ethyl acetate and water employed according to the present invention must at least substantially correspond to the following equation:

(Molar concentration of the ethyl alcohol) X (molar concentration of the acetic acid) :1 (Molar concentration of the ethyl acetate) M (molar concentration of the water) The composition of such equilibrium solvent mixture according to the invention can, for example, be calculated as follows when the mixture is to contain 9% of weight of water and 2% by weight of acetic acid employing the following equations:

X (A) (I) (E) X .11 88.(E)+9+46.(A) +2=1oo United States Etent G 2,970,032 Patented Jan. 31, 1961 the solvent mixture corresponding to a stationary equilibrium is as follows:

, Percent Acetic acid 2 Water 9 It is not absolutely necessary that the concentrations of the solvent mixture be maintained with the greatest exactitude in accordance with calculated quantities for the equilibrium mixture, but the best results are obtained with the exact quantities. The further the quantities deviate from those theoretically required for the equilibrium mixture, the less stable the solutions of tanninboric acid compounds prepared therewith are.

The tannin-boric acid compounds employed according to the invention can be prepared according to the procedures described in application S.N. 192,633, filed October 27, 1951. For example, the following procedures can be employed:

(a) 25.5 parts by weight of pure tannin and 4.5 parts by weight of boric acid are dissolved in 70 parts by weight of ethyl alcohol (96 vol. percent). After the solution has been allowed to stand at v room temperature (about 20 C.) for one hour the ethyl alcohol is removed by distillation and the residue remaining is a compound of boric acid and tannin. Other inert solvents, such as, for example, acetone, can be employed instead of the ethyl alcohol indicated.

The equilibrium solvent mixture of acetic acid, ethyl alcohol, ethyl acetate and water according to the inven- EXAMPLE l 7 parts by weight of tannin and 3 parts by weight of boric acid were dissolved in a mixture of 1.8 parts by Weight of acetic acid, 8.1 parts of water, 53.1 parts of ethyl alcohol and 27.0 parts of ethyl acetate and the resulting solution was boiled under reflux for 1 hour. The resulting clear solution of the tannin-boric acid compound produced was stable and could be stored for any desired length of time without decomposition. The solution was of the following composition:

Percent by wt. Tannin-boric acid compound 10 Acetic acid 1.8

Water e 8.1 Ethyl alcohol 53.1 Ethyl acetate 27.0

Patch tests on human patients (50) on healthy skin revealed no sign of non-compatability with the patients tested.

The solution was also clinically tested on 30 cases of onychomycosis (caused by ringworms and germs) of varying degrees of severity, ranging from (1) patients having one or more nails indicating a beginning of an onychomycosis in the form of a discoloration of apart of the nail, (2) patients having nails already partly split or de formed and (3) patients having nails in which the whole nail was swollen and deformed.

When the lesions on the nails of the patients were slight the nails were given no pretreatment before application of the solution according to the invention. When the lesions were more severe, the nails were pretreated with a 5% alcoholic caustic potash solution until slight maceration occurred (about minutes) and then rinsed with water and painted with the solution according to the invention. The number of applications of the solution according to the invention was twice daily except in instances where the patients work required them to come into contact with water repeatedly, the patients were requested to make several additional applications daily. The following table gives the results attained:

Table I Number patients treated Cured Improved The treatment of the less serious cases required about 4 weeks and the more serious required several months. The two patients with incurable onychomycosis were seriously infected cases having suffered lesions involving all nails for 4 and 12 years, respectively. -The causal organism in these two cases was Candida albicans.

The preferred concentrations of the tannin-boric acid compound in the solutions according to the invention lie ganismEpiderm0phyton inguinale) and eczema mycotica (causal organismvarious ringworms and germs) were treated with such a 5% solution. The patients treated were divided into three groups according to severity of the disease, namely:

Group 1: Single seat (foci) of disease up to a diameter of 2 cm.

Group 2: Single larger foci.

Group 3: Several larger foci or several foci of long standing andresistant to other therapy. 7

The treatment consisted of painting the solution on the A diseased areas twice daily for about 2 to 4 weeks in the case of the patients of Group 1, increasing up to 14 weeks for patients in Group 3.

The following table gives the results attained:

Table II Number No impa-tients Cured Improved provetreated ment 31 24 7 21 12 8 1 Group 3 13 7 3 3 The patients in which no improvement occurred were for tanning animal skins, especially for the production 4 of light fine leathers. The following example illustrates the preparation of a leather tanning solution suitable for tanning leather:

EXAMPLE 2 An equilibrium solvent mixture was prepared by mixing 23.60 kg. of ethyl acetate, 1.80 kg. of water, 61.93 kg. of 96% ethyl alcohol and 0.99 kg. of acetic acid. 11.68 kg. of the tannin-boric acid compound prepared as described above under (a) were then dissolved therein.

The following procedure was employed to employ such solution in tanning kip skins:

Limed kip skins which were still moist were repeatedly immersed in alcohol of increasing concentration (starting concentration 50%) to remove the moisture contained therein and dried at a temperature below 40 C. to drive off the alcohol retained. The thus dried skins were then tanned in the tanning solution for six hours.

While several illustrations of equilibrium solvent mixtures have been given by way of example, the proportions of the components of such equilibrium mixture can be varied as long as they at least substantially conform with the quantities required for a stationary equilibrium at the prevailing temperature and as long as the quantity of acetic acid in such equilibrium mixture does not exceed 4%.

The solvent mixture employed in Example 1 for the production of the tannin-boric acid compound solution can be distilled off from such solution to leave the tanninboric acid compound. The recovered distilled solvent mixture has the same concentration as the original mixture, namely, acetic acid 2% by wt., water 9% by wt., ethyl alcohol 59% by wt. and ethyl acetate 30% by wt., and can be reused for the production of further quantities of tannin-boric acid compounds.

This application is a continuation-in-part of my eopending application Serial No. 256,375, filed November 14, 1951, now abandoned.

Instead of pure tannin there also can be used commercial tannins of various kinds as starting material. It is also possible to employ the boric acid excess but in this case the surplus remains unchanged.

I claim:

1. A tanning solution comprising a substantially stable clear solution of a tannin-boric acid compound in an equilibrium solvent mixture of ethyl acetate, ethyl alcohol, acetic acid and water in such proportions as to satisfy the equation (Molar concentration of acid) X (molar concentration of alcohol) y 4 (Molar concentration of ester) X (molar concentration of water) the quantity of acetic acid in said equilibrium solvent mixture not exceeding 4%.

2. A tanning solution according to claim 1 which contains 5 to 15% of the tannin-boric acid compound.

References Cited in the file of this patent UNITED STATES PATENTS 9,125 Keil July 7, 1942 OTHER REFERENCES Brewster: Organic Chemistry, 1948, Prentice-Hall 

1. A TANNING SOLUTION COMPRISING A SUBSTANTIALLY STABLE CLEAR SOLUTION OF A TANNIN>BORIC ACID COMPOUND IN AN EQUILIBRIUM SOLVENT MIXTURE OF ETHYL ACETATE, ETHYL ALCOHOL, ACETIC ACID AND WATER IN SUCH PROPORTIONS AS TO SATISFY THE EQUATION 